Fabrication Process and Thermoelectric Properties of CNT/Bi 2

Carbon nanotube/bismuth-selenium-tellurium composites were fabricated by consolidating CNT/Bi2(Se,Te)3 composite powders prepared from a polyol-reduction process. The synthesized composite powders exhibit CNTs homogeneously dispersed among Bi2(Se,Te)3 matrix nanopowders of 300 nm in size. The powders were densified into a CNT/Bi2(Se,Te)3 composite in which CNTs were randomly dispersed in the matrix through spark plasma sintering process. The effect of an addition of Se on the dimensionless figure-of-merit (ZT) of the composite was clearly shown in 3 vol.% CNT/Bi2(Se,Te)3 composite as compared to CNT/Bi2Te3 composite throughout the temperature range of 298 to 473 K. These results imply that matrix modifications such as an addition of Se as well as the incorporation of CNTs into bismuth telluride thermoelectric materials is a promising means of achieving synergistic enhancement of the thermoelectric performance levels of these materials

Effect of the ENEPIG Process on the Bonding Strength of BiTe-based Thermoelectric Elements

To improve the mechanical performance of BiTe-based thermoelectric modules, this study applies anti-diffusion layers that inhibit the generation of metal intercompounds and an electroless nickel/electrode palladium/mission gold (ENEPIG) plating layers to ensure a stable bonding interface. If a plated layer is formed only on BiTe-based thermoelectric, the diffusion of Cu in electrode substrates produces an intermetallic compound. Therefore, the ENEPIG process was applied on the Cu electrode substrate. The bonding strength highly increased from approximately 10.4 to 16.4 MPa when ENEPIG plating was conducted to the BiTe-based thermoelectric element. When ENEPIG plating was performed to both the BiTe-based thermoelectric element and the Cu electrode substrate, the bonding strength showed the highest value of approximately 17.6 MPa, suggesting that the ENEPIG process is ef-fective in ensuring a highly reliable bonding interface of the BiTe-based thermoelectric module

Degreasing Efficiency of Electroplating Pretreatment Process Using Secondary Alcohol Ethoxylate as Nonionic Surfactant

In this study, the effect of the hydrophilic–lipophilic balance (HLB) number and cloud point (CP) of a secondary-alcohol ethoxylated nonionic surfactant on degreasing efficiency was investigated. A degreasing process was conducted for steel samples with different surfactants in a degreasing solution. The HLB number and CP increased with the increasing n of the hydrophilic ethylene oxide (OCH2CH2)n group. For a constant temperature of the degreasing solution (30–80 °C), the degreasing efficiency was investigated as a function of degreasing time. The highest degreasing efficiency was observed near the cloud point of the surfactant, and the degreasing efficiency decreased significantly at temperatures lower and greater than the cloud point. A Hogaboom test was carried out to observe oil stains on the surface of samples. Additionally, the contact angle of the surface with water droplets was measured after degreasing with various surfactants

Enhanced Energetic Performance of Polyvinylidene Fluoride-Coated Zirconium Particle

In this study, energetic behaviors of polyvinylidene fluoride (PVDF)-coated zirconium (Zr) powders were investigated using thermogravimetric analyzer-differential scanning calorimetry (TGA-DSC). PVDF-coated Zr powder had 1.5 times higher heat flow than ZrO2-passivated Zr powder. PVDF-coated Zr powder had a Zr-F compound formed on its surface by its strong chemical bond. This compound acted as an oxidation-protecting layer, providing an efficient combustion path to inner pure Zr particle while thermal oxidation was progressing at the same time. PVDF coating layers also made thermal reaction start at a lower temperature than ZrO2-passivated Zr powder. It was obtained that the surface PVDF coating layer evaporated at approximately 673 K, but the surface oxide layer fully reacted at approximately 923 K by DSC analysis. Hence, Zr powders showed enhanced energetic properties by the PVDF-coated process

Preparation of Ni-Coated Si Anode Materials Using Electroless Plating for High Performance Secondary Lithium-Ion Batteries

In this paper, we introduce an electroless plating technique to synthesize uniform metal nanoparticles on silicon (Si) powders that provide electrical pathways on Si anodes in lithium-ion batteries (LIBs). Scanning electron microscopy images reveal that hemispherical Ni nanoparticles are conformally deposited on Si powders. The electrochemical performances show that the rate capability and cyclability of Ni-coated Si are much better than bare Si electrodes. Electrochemical impedance spectroscopy and powder resistance measurements confirm that electroless plating enhances electrical conductivity by coating Ni nanoparticles on a Si anode, which leads to excellent electrochemical performances. Our approach provides a simple and effective route to prepare high-performance anode materials with large mass for future LIB applications. Copyright © 2017 American Scientific Publishers All rights reserved.1

Binder–free of NiCo–Layered Double Hydroxides on Ni–coated textile for Wearable and Flexible Supercapacitors

Recently, the combination of nickel (Ni) and cobalt (Co) binary hydroxides have been regarded as a promising class of materials due to their excellent redox reversibility and relatively high capacity. In this work, we demonstrate Ni and Co layered double hydroxides (NiCo–LDHs) on Ni–coated textile for wearable supercapacitor (SC) applications. Ni–coated textile was used as flexible current collector and NiCo–LDH nanosheets were deposited on textile as a pseudocapacitive materials. The electrochemical performances of NiCo–LDHs have been evaluated and optimized by varying the mole ratio of Ni and Co via hydrothermal process. The NiCo–LDH electrodes with Ni:Co ratio of 3:7 has the maximum specific capacitance, which is attributed to the CoOOH by improving the conductivity and enlarged interlayer spacing with intercalation of NO3 −. Moreover, solid–state NiCo–LDH SC exhibits a maximum volumetric energy density of 1.25 mWh cm−3 at a power density of 47.4 mW cm−3. © 2018 Elsevier B.V.1

Sn-Pd-Ni Electroplating on Bi2Te3-Based Thermoelectric Elements for Direct Thermocompression Bonding and Creation of a Reliable Bonding Interface

The Sn-Ag-Cu-based solder paste screen-printing method has primarily been used to fabricate Bi2Te3-based thermoelectric (TE) modules, as Sn-based solder alloys have a low melting temperature (approximately 220°C) and good wettability with Cu electrodes. However, this process may result in uneven solder thickness when the printing pressure is not constant. Therefore, we suggested a novel direct-bonding method between the Bi2Te3-based TE elements and the Cu electrode by electroplating a 100 μm Sn/ 1.3 μm Pd/ 3.5 μm Ni bonding layer onto the Bi2Te3-based TE elements. It was determined that there is a problem with the amount of precipitation and composition depending on the pH change, and that the results may vary depending on the composition of Pd. Thus, double plating layers were formed, Ni/Pd, which were widely commercialized. The Sn/Pd/Ni electroplating was highly reliable, resulting in a bonding strength of 8 MPa between the thermoelectric and Cu electrode components, while the Pd and Ni electroplated layer acted as a diffusion barrier between the Sn layer and the Bi2Te3 TE. This process of electroplating Sn/Pd/Ni onto the Bi2Te3 TE elements presents a novel method for the fabrication of TE modules without using the conventional Sn-alloy-paste screen-printing method

Effect of Pd-P Layer on the Bonding Strength of Bi-Te Thermoelectric Elements

In this study, the effect of electroless Pd-P plating on the bonding strength of the Bi-Te thermoelectric elements was investigated. The bonding strength was approximately doubled by electroless Pd-P plating. Brittle Sn-Te intermetallic compounds were formed on the bonding interface of the thermoelectric elements without electroless Pd-P plating, and the fracture of the bond originated from these intermetallic compounds. A Pd-Sn solder reaction layer with a thickness of approximately 20 μm was formed under the Pd-P plating layer in the case of the electroless Pd-P plating, and prevented the diffusion of Bi and Te. In addition, the fracture did not occur on the bonding interface but in the thermoelectric elements for the electroless Pd-P plating because the bonding strength of the Pd-Sn reaction layer was higher than the shear strength of the thermoelectric elements